This invention relates to a stroke cushioning means for a hydraulic cylinder adapted to slow down and stop a piston at the stroke ends thereof.
There has heretofore been employed a rod-side stroke cushioning means wherein a sleeve is fitted from outside to a portion of the piston rod near the piston and a cushion ring is fitted on the side of one end of the cylinder to restrict the fluid flow between the cushion ring and the sleeve. In the above-mentioned prior art cushion ring, since it is difficult to align the center line of the cushion ring through which the sleeve is moved forwards and backwards with that of the hydraulic cylinder, it is necessary to fit the cushion ring inside the cylinder in such a manner that it can be moved to some degree and then secure the cushion ring by means of a snap ring. Such snap ring has been disadvantageous in that since it has a notch formed in part of the circumferential portion thereof, noise tends to generate in the notch when part of the fluid under pressure confined therein is discharged into the passage thereby damaging the snap ring quickly.
Whilst, there has heretofore been employed a cylinder-head end stroke cushioning means wherein a plunger is fitted to the leading end of a piston rod to obtain a cushioning effect. This type of plunger has, however, been disadvantageous in that because it is difficult to align the center line of the passage in which the plunger is moved forwards and backwards with that of the cylinder, it is necessary to fit the plunger to the piston rod so that the plunger can be moved relative to the piston rod to some degree thereby complicating the structure of the component parts.